Pneumatic control



Aug. 14, 1945. c BRAMMER ETAL 2,382,853

PNEUMATIC CONTROL Filed April 12, 1.945

Inventors A ltorney:

Patented ae is, 194s UNITED s'rATi-is PATENT I or ies amass 'PNEUMATIC CONTROL Thames Board Mills land, aBritisli company Limited, Purileet, Eng- Application April 12, 1948, Serial No; 482,818

' In Great Britain February 14, 1942 2 Claims. (01. 187-139) The. present invention relates to a pneumatic control for a pressure device which may be used in maintaining consistency of a viscous liquid, or semi-liquid, or density of a liquid, that is to say of liquids containing solid matter in solution orsuspension.

In many industries it is particularly desirable to provide automatic means whereby the consistency of a'liquid or semi-liquid under treatment in an industrial process can be maintained constant.

For instance, in the artificial silk industry it is desirable that the viscosity of the liquid passing through the spinning jets be maintained constant, and again in the paper industry it is highly desirable that the consistency of pulp in the manufacture of board or paper be maintained constant to avoid irregularity in stren th or thickness of the board or paper web.

It is known to maintain constancy of consistency by adding or reducing the amount of fluid forming the medium of solution or of the fluid carrying the suspension of solid matter, or in other cases by increasing or decreasing the temperature of the fluid stream, according to the flow gradient of said liquid between two spaced points in an open vessel.

An object of the present invention is to provide a pneumatic control for controlling and damping of such arrangements and effects for preventing sudden changes in the consistency or density of the fluid stream.

According to the present invention the pneumatic control operated by an alteration in difference of flow gradient or density between two spaced points in the fluid stream does not operate means for adding a variable amount of liquid to said fluid stream directly but indirectly through damping means so that the quantity of liquid bein added per unit time can only be varied at a slow rate.

The invention will be more particularly described with reference to the accompanying drawing, in which:

Figure 1 shows the application of the invention to the control of consistency of paper pulp in the manufacture of board or paper.

Figure 2 shows a modified arrangement suitable for control of the consistency of a solution. In the drawing, the invention is illustrated in connection with apparatus for controlling the density of paper P p- Paper pulp, taken by way of example, is circulated by means of a pump i from an inlet pipe 2 to an outlet pipe 3. leading to a sump 4 in a flow box 5, the material passing over a weir 8 and flowing out from the outlet 1 on the flow box remotely situated to the weir I. the level of the liquid due to its viscosity or density taking coupled to a common air pressure lead I4. Compressed air ted to the line M will therefore bubble out from the lower ends of the standpipes l0 and II and, as the static head of stun or pulp immediately outside these standpipes III, II, will difler, the pressure in these standpipes 10, II, will also differ, this diii'erence of pressure being communicated by pipe line connections l5, It, to a differential controller formed of intercommunicating vessels [8, l9, containing liquid; a movable element 20 in one vessel being connected by linkage ii to a lever 22 operating a throttle valve 23 on an air bleed port 24 of an air line 28. The link 2! may also be connected to visual indicator 26, moving over a scale 21, so that the degree oi consistency, being a factor of the flow gradient 8, can be read 01! thereon.

As there will be a time lag equivalent to the time taken by pulp to pass from the inlet point 29 where it receives free liquid from the pipe to the time when it reaches the standpipe ll, hunting would occur if the pipe 25 was directly coupled to the diaphragm chamber 41. To avoid this the bleed valve 23, 24, is not connected directly to the pipe 46 but indirectly through a damping device which may conveniently be in th form of a pair of interconnected vessels 30, 30, the pipe connectin them being provided with a throttle valve 30. The valve 24 is connected by pipe 25 with one vessel 30" whilst the other 30 is connected to a Bourdon pressure tube ll operating a lever 32 carrying a throttle valve 33 co-operating with a bleed valve 34 on the air pressure line 46.

It will be preferred to provide means to adjust the position 01 one or both of the standpipes III, II along the flow box, for instance by providing a graduated scale 31 on the side of the flow box, so that the device can be adjusted to suit various grades of material, such as paper pulp to be controlled, and at the same time maintain them at a constant consistency as indicated upon the scale 21 or on a graph recorder. Once this setting is adjusted to a required condition of the material consistency can then be controlled and any variations will be evident upon the scale 21 or on the graph recorder. Should the device be required to operate on a wholly diflerent material an ad-' justment oi the settlns of scale 21 may be necessary.

In the modified arrangement of Figure 2 more particularly suitable to thecontrol of density of a liquid medium having matter in solution, the" pressure line is connected to a pair of standpipes 48, 49, one of which is .displaceable' vertically as compared with horizontally in the case of Figure 1, when it is desired to adjust the set value of the density it is desired to maintain constant. An adjustment of one pipe vertically relatively to the aseaess tarding the application of the control pressure to the relay pressure establishing means comprising a pair of vessels having their upper ends respectively connected with the control conduit in a manner to transmit pressure from one portionthereoi to another portion, the lower portions of said vessels containing liquid and being in communication through a conduit having adjustable restricting means.

other on the scale ill provides for an adjustment 2. In a pneumatic controlsystem for operating a pressure responsive device, a control-pressure conduit, means for establishiril a control pres- 'sure in said conduit which vai'ies in accordance with a variable condition, means responsive to the control pressure including a bleed valv and a Bourdon pressure tube for operating the same for establishing a relay pressure proportional to the control pressure, means for retarding the application 01' the control pressure to the relay pressure establishing means comprising a pair 0! vessels having their upper ends respectively connected with the control conduit in a manner to transmit pressure from one portion thereof to another portion, the lower portions of said vessels containing 5 liquid and being in communication through a conduit having adjustable restricting means.

FREDERICK CHARLES B WILLIAM CHARLES HUBERT WEST. 

